CFP - Docs - mKeepFirst

mKeepFirst

(num: number) => (anArray: array) => anArray

Keep the first num elements of an array

Consider keepFirst instead.
This is for the uncommon case where mutating anArray is required.

Try It

const mKeepFirst2 = mKeepFirst(2)

const arr = [1, 2, 3, 4]
const mutatedArr = mKeepFirst2(arr)
console.log(mutatedArr === arr) // is true
console.log(arr) // is [1, 2]
const mKeepFirst2 = mKeepFirst(2)

const arr = [1, 2, 3, 4]
const mutatedArr = mKeepFirst2(arr)
console.log(mutatedArr === arr) // is true
console.log(arr) // is [1, 2]

Try It

const mKeepFirst2 = mKeepFirst(2)

const arr = [1, 2, 3, 4]
const mutatedArr = mKeepFirst2(arr)
console.log(mutatedArr === arr) // is true
console.log(arr) // is [1, 2]
const mKeepFirst2 = mKeepFirst(2)

const arr = [1, 2, 3, 4]
const mutatedArr = mKeepFirst2(arr)
console.log(mutatedArr === arr) // is true
console.log(arr) // is [1, 2]

Sometimes we have ordered data and only care about the first elements. Below, we have the top 5 women of the Paris Olympics Single Canoe Slalom event. Let's find the medalists.

Try It

const canoeSlalomResults = [
  { name: 'jessica', time: 101.06 },
  { name: 'elena', time: 103.54 },
  { name: 'evy', time: 109.95 },
  { name: 'zuzana', time: 111.07 },
  { name: 'ana', time: 112.7 },
]

const keepMedalists = mKeepFirst(3)
keepMedalists(canoeSlalomResults)
const getNames = mapValues(get('name'))
const medalists = getNames(canoeSlalomResults)
console.log(medalists)
// is [
//  jessica
//  elena
//  evy
// ]
type Result = {
  name: string
  time: number
}

const canoeSlalomResults: Result[] = [
  { name: 'jessica', time: 101.06 },
  { name: 'elena', time: 103.54 },
  { name: 'evy', time: 109.95 },
  { name: 'zuzana', time: 111.07 },
  { name: 'ana', time: 112.7 },
]

const keepMedalists = mKeepFirst(3)<Result[]>
keepMedalists(canoeSlalomResults)
const getName = get('name')<Result>
const getAllNames = mapValues(getName)<Result[]>
const medalists = getAllNames(canoeSlalomResults)
console.log(medalists)
// is [
//  jessica
//  elena
//  evy
// ]

Try It

const canoeSlalomResults = [
  { name: 'jessica', time: 101.06 },
  { name: 'elena', time: 103.54 },
  { name: 'evy', time: 109.95 },
  { name: 'zuzana', time: 111.07 },
  { name: 'ana', time: 112.7 },
]

const keepMedalists = mKeepFirst(3)
keepMedalists(canoeSlalomResults)
const getNames = mapValues(get('name'))
const medalists = getNames(canoeSlalomResults)
console.log(medalists)
// is [
//  jessica
//  elena
//  evy
// ]
type Result = {
  name: string
  time: number
}

const canoeSlalomResults: Result[] = [
  { name: 'jessica', time: 101.06 },
  { name: 'elena', time: 103.54 },
  { name: 'evy', time: 109.95 },
  { name: 'zuzana', time: 111.07 },
  { name: 'ana', time: 112.7 },
]

const keepMedalists = mKeepFirst(3)<Result[]>
keepMedalists(canoeSlalomResults)
const getName = get('name')<Result>
const getAllNames = mapValues(getName)<Result[]>
const medalists = getAllNames(canoeSlalomResults)
console.log(medalists)
// is [
//  jessica
//  elena
//  evy
// ]